On 1/31/22 04:38, Michal Hocko wrote:
On Sat 29-01-22 15:53:15, Waiman Long wrote:
It was found that a number of offlined memcgs were not freed because
they were pinned by some charged pages that were present. Even "echo
1 > /proc/sys/vm/drop_caches" wasn't able to free those pages. These
offlined but not freed memcgs tend to increase in number over time with
the side effect that percpu memory consumption as shown in /proc/meminfo
also increases over time.
In order to find out more information about those pages that pin
offlined memcgs, the page_owner feature is extended to dump memory
cgroup information especially whether the cgroup is offlined or not.
It is not really clear to me how this is supposed to be used. Are you
really dumping all the pages in the system to find out offline memcgs?
That looks rather clumsy to me. I am not against adding memcg
information to the page owner output. That can be useful in other
contexts.
I am just piggybacking on top of the existing page_owner tool to provide
information for me to find out what pages are pinning the dead memcgs.
page_owner is a debugging tool that is not turned on by default. We do
have to add a kernel parameter and rebooting the system to use that,
but that is pretty easy to do once we have a reproducer to reproduce the
problem.
Cheers,
Longman
